The thesis introduction talk about ABC transporters and their structures, P-glycoprotein and its mechanism of action, Cancer multidrug resistance, substrates, and inhibitors, The physiological role of Pgp, its expression and function in the immune cell populations, and its impact on the immune cells in cancer.In this work, our primary focus was on the evaluation of the Physiological expression of Pgp in human T lymphocytes, particularly in the primary human cytotoxic T lymphocytes (CTLs), besides its expression in two other lymphoid origin human tumor cell lines derived from hematological malignancies of the CD4+ Jurkat and the CD8+ TALL-1.Cells used were Primary human cytotoxic T lymphocytes, Jurkat, TALL-1, NIH 3T3 cells and NIH 3T3 MDR1 cells. Fluorescence microscopy and Flow cytometry were used to assay the calcein accumolation inside these cells with and without cyclosporin A.